1. Field of the Invention
The present invention relates to a steering device, and more particularly to an electrical power assisted steering device for a vehicle.
2. Description of Related Art
A steering device of a vehicle is mounted between a steering wheel and wheels of the vehicle. The steering device has an upper shaft, a lower shaft engaged with the upper shaft by threads, and a detecting unit. The upper shaft is connected with the steering wheel. The lower shaft is connected with the wheels. An end of the lower shaft opposite to the upper shaft is engaged with an upper rotor of the detecting unit. When the lower shaft is driven to rotate by the upper shaft, the upper rotor of the detecting unit is also driven to rotate. Then, a lower rotor of the detecting unit can detect a rotating angle of the upper rotor, and then a motor is driven to operate. The motor can drive the upper shaft and the lower shaft to rotate in the same direction to provide a steering assist for a user.
However, the upper shaft and the lower shaft are engaged with each other by threads, and the threads may be worn and damaged after use for a period. When the threads between the upper shaft and the lower shaft are worn or damaged, a torsion force formed by the steering device may be changed, and the operation of the steering wheel for the user may be badly affected.